| ( | X | − | 40 | ) | ( | 200 | − | 2 | X | ) | = | 1350 |
| Left side of the equation = | X | ( | 200 | − | 2 | X | ) | − | 40 | ( | 200 | − | 2 | X | ) |
| = | X | × | 200 | − | X | × | 2 | X | − | 40 | ( | 200 | − | 2 | X | ) |
| = | 200 | X | − | X | × | 2 | X | − | 40 | × | 200 | + | 40 | × | 2 | X |
| = | 200 | X | − | X | × | 2 | X | − | 8000 | + | 80 | X |
| = | 280 | X | − | X | × | 2 | X | − | 8000 |
| 280 | X | − | X | × | 2 | X | − | 8000 | = | 1350 |